I Can't insert multiple values for a Multiple Select field (script)

I'm trying set multiple values for a Multiple Select field but I can't, ever sends the Error Invalid reference key [null]. Please I need help this is my script...

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for (var j=0; j<TarSigts.length; j++){
  TarSigt = new Array();
  TarSigt = nlapiGetFieldValue('custevent_task_scsras'); 
  TarSigt = TarSigt.split(" ");    
  filter[0] = new nlobjSearchFilter('internalid', null, 'is', TarSigt, null); 
  columns[0] = new nlobjSearchColumn('custrecord_task_rspnsble');
  columns[1] = new nlobjSearchColumn('custrecord_task_ntfy');
  columns[2] = new nlobjSearchColumn('altname');
  columns[3] = new nlobjSearchColumn('custrecord_task_sncrnia');
  columns[4] = new nlobjSearchColumn('custrecord_prcess_trea_sgnte');   
  result = nlapiSearchRecord('customrecord_process_tasks', null, filter, columns ); 
  var idC = nlapiGetFieldValue('company');
  var x = getUserName(idC);